Bump lxml from 4.5.2 to 4.6.2

Bumps [lxml](https://github.com/lxml/lxml) from 4.5.2 to 4.6.2.
- [Release notes](https://github.com/lxml/lxml/releases)
- [Changelog](https://github.com/lxml/lxml/blob/master/CHANGES.txt)
- [Commits](lxml/lxml@lxml-4.5.2...lxml-4.6.2)

Signed-off-by: dependabot[bot] <support@github.com>

requirements.txt

@@ -51,7 +51,7 @@ jupyter-server-proxy==1.5.0
 jupyterlab==2.1.5
 jupyterlab-server==1.2.0
 kiwisolver==1.2.0
-lxml==4.5.2
+lxml==4.6.2
 MarkupSafe==1.1.1
 matplotlib==3.2.2
 mergedeep==1.3.0